This invention relates generally to light-emitting silicon structures and silicon-based photonic devices. In greater particularity, the invention pertains to light-emitting laterally disposed nanostructures of silicon and silicon-based photonic devices made of laterally disposed nanostructures of silicon.
Silicon is the mainstay of the semiconductor integrated circuit industry because of its process maturity, low cost, high yield and high reliability. Its use has been limited, however, in optoelectronic applications by its 1.1 electron-volt (eV) indirect band gap structure which yields only very weak infrared luminescence. As a result, light-emitting devices have been made of Group III-V semiconductors, such as GaAs. Unfortunately such semiconductors cannot be readily integrated with silicon-based electronic technology, which has become well established and comparatively cheap.
The availability of a light-emitting/photonic silicon source would allow a breakthrough in optoelectronic integrated circuits, having applications in optical computing, high-speed communications, and integrated sensor and smart sensor technology. Additional applications could include light-emitting diodes (LEDs), flat-panel displays, and optical interconnections. If these silicon based light-emitting/photonic devices could be monolithically integrated with other structures on silicon, a tremendous advance in silicon-based electronics could be made.
The discovery of photoluminescent porous silicon has caused porous silicon to emerge as a potential photonic source compatible with silicon microelectronics. The porous silicon is of high porosity with very thin remaining wire-like structures that are supported by their ends, these structures sometimes are referred to as quantum wires, see L. T. Canham, Appl. Phys. Let., 57, 1046 (1990). The interest in integrating silicon circuitry with silicon light-emitting (photonic) devices has resulted in the application of porous silicon to electroluminescent devices, see A. Richter, P. Steiner, F. Kowlowski, and W. Lang, IEEE Elect. Dev. Lett., 12, 691 (1991).
Many theories on the origin of the silicon-based bright visible light emission abound, the best supported theory being the quantum confinement model. This model has been validated by theoretical calculations that predict higher direct energy band gaps as cross sectional wire dimensions decrease into the nanoscale regions, see V. Lehman and U. Gosele, Appl. Phys. Lett., 58, 856 (1991); F. Koch, V. Petrov-Koch, and T. Muschik, J. of Luminescence, 57, 271 (1993); G. D. Sanders and Y. -C. Chang, Phys. Rev. B, 45(16) (1992) 9202; and T. Ohno, K. Shiraishi and T. Ogawa, Phys. Rev. Lett. 69(16) (1992) 2400. Research in the field has attempted to verify these predications by fabricating vertical nanowire structures (columns) in bulk silicon and measuring the photoluminescent light output of these columns, see H. I. Liu, N. I. Maluf, R. F. W. Pease, D. K. Biedelsen, N. M. Johnson, F. A. Ponce, J. Vac. Sci. Technol. B, 10(6) (1992) 2846.
Practical device structures of either porous silicon quantum wires or of silicon vertical columns have however been unattainable in part due to the difficulty of precise control of nanostructured dimensions as well as due to difficulties in making efficient electrical contact to the fragile nanostructures.
Other quantum effect devices, such as the lateral resonant tunnelling field-effect transistors, have been modeled in GaAs and AlGaAs, see S. Y. Chou, J. S. Harris and R. F. W. Pease, Appl. Phys. Lett., 52(23) (1988) 1982. However effectively implementing such lateral nanostructures in a silicon-based technology has not yet been achieved in the prior art.
A need exists for silicon-based nanostructures whose dimensions are precisely controlled for optimizing light-emitting properties, whose structure is well supported to decrease nanostructure breakage, whose configuration is amenable to the making of good electrical connection, and whose material make-up is compatible with other silicon-based electronics.